Asthma is the most common chronic disease of childhood in the developed world, and its prevalence in Western industrialized countries is increasing at an alarming rate. Maternal diet during pregnancy represents an important exposure with significant potential to modify immune function in offspring and hence the development of asthma and related atopic disorders in childhood. In addition, fetal growth may be a marker of prenatal processes that have large impact on asthma risk. Fetal growth is now known to be an indicator for risk of other chronic diseases, but the data regarding asthma are remarkably sparse. The goals of this application are to examine the potential impact of maternal dietary factors during pregnancy on the development of asthma and related disorders in early childhood, and to clarify the relationship between size at birth and incident asthma. A longitudinal prospective study is the most appropriate study design to evaluate these goals. This application takes advantage of the resources provided by Project Viva, an ongoing prospective cohort study of pregnant women and their infant offspring among members of Harvard Pilgrim Health Care, a large managed care organization in New England. Data already available from Project Viva include detailed dietary data on mother and infant, along with data on anthropometric, social, environmental, demographic, economic, psychological, and lifestyle variables. By following the Project Viva cohort until the ages of 3-4 years, the current application provides a relatively economical way to obtain updated exposure and outcome data and to answer scientific questions of major public health importance. This work also brings together a multidisciplinary research team with a proven track record of collaboration and expertise in nutritional, respiratory, and pediatric epidemiology.